Polarity

Low-resistance measurement proving that conductors which must be complete actually are. That means protective conductors back to the earthing terminal, bonding conductors to services, and the legs of ring final circuits. Performed dead with a low-ohm meter, it is the first step of the test sequence because everything after it assumes the earth path exists.

The procedure that proves a circuit dead before anyone works on it. Prove the voltage indicator against a known source, isolate the circuit, secure the isolation with your own lock and tag, prove the point of work dead across all conductor combinations, then prove the indicator again. The final step is the one that catches a tester that died mid-job.

The earth wire of a circuit. It links the metal parts of the equipment the circuit feeds back to the main earthing terminal. It is not the normal load-current return path, although equipment can produce protective-conductor current in normal operation. During an earth fault it provides a path for fault current, working with the earthing arrangement and protective device to achieve disconnection. In UK wiring it is green and yellow, or bare inside twin-and-earth cable, with green-and-yellow sleeving wherever it is exposed.